PZT (lead zirconate titanate) and PLZT (lead lanthanum zirconate titanate) films are used in integrated circuit to form the dielectric in high performance capacitors. These films are typically formed using sol-gel technology.
Sol-gel spin coating technology is frequently used for the fabrication of metal oxides such as PZT and PLZT using metal alkoxide precursors. A solution (sol) containing the metal alkoxide precursors is spin coated onto the wafer to form a thinfilm of PZT or PLZT with uniform thickness. A low temperature bake is then performed to remove some of the solvent and to convert the metal alkoxides to a gel. During this step significant densification and shrinkage may occur. A final high temperature anneal may be performed to cause chemical reactions converting the metal alkoxides to metal oxides.
Formation of a PZT or PLZT capacitor dielectric film is accomplished using a spin coater such as is shown in FIG. 1. A wafer 106 is placed on the spinner 102 and the PZT or PLZT containing solution is dispensed onto the center of the wafer through a nozzle 104. The wafer 106 is then spun at high speed to distribute the PZT or PLZT containing solution across the wafer to form a thinfilm of PZT or PLZT with uniform thickness. The nozzle 104 then moves to the edge of the wafer and a solvent such as butanol which dissolves PZT or PLZT is used to remove the PZT or PLZT thinfilm from the edge of the wafer (edge-bead removal). Edge bead removal eliminates the formation of particles at the edge of the wafer that cause defects and reduce yield.
During the edge bead removal process some of the solvent such as butanol is adsorbed into the exposed edge of the PZT or PLZT thinfilm causing it to swell. During the subsequent bake and anneal, the swelled PZT or PLZT thinfilm may delaminate resulting in particle defects and reduced yield.